There is an in-vehicle device known in the related art that captures an image of an area ahead of a vehicle via a camera installed at the vehicle, executes edge detection so as to detect a horizontal edge in the captured image and detects a lane mark (a lane demarcation line) on the road surface (PTL1). This device extracts a pixel, at which the absolute value representing the luminance difference between the luminance value thereof and the luminance value at a pixel adjacent to the pixel along the horizontal direction exceeds a threshold value, as an edge point and recognizes a lane mark based upon the number of such edge points.
In addition, there is a method known in the related art through which foreign matter or the like settled on an in-vehicle camera lens is detected by detecting, based upon the state of the in-vehicle camera lens, an immobile area in a captured image that remains immobile even while the vehicle is traveling (PTL2). There is also a method known in the related art through which a decision is made that water drops are present by using an overlapping image-capturing region shared by a plurality of cameras (PTL3).